1. Technical Field
The present invention relates to a lens barrel including an eccentricity adjusting mechanism, in particular, to a lens barrel including an eccentricity adjusting mechanism for improving optical performance (a resolution level or others) by adjusting a position of a predetermined lens constructing an optical system of the lens barrel in a direction orthogonal to an optical axis.
2. Related Art
Generally, in case of a lens barrel for use in a TV camera or others for broadcasting or business, the adjustment of eccentricity of a lens to increase optical performance such as MTF (resolution) is carried out while the image formation state (image quality) of the lens is observed by a collimator attached onto a leading end of the lens after the lens is fitted into the lens barrel (inside a fixed barrel). The adjustment of eccentricity of a lens is realized by carrying out position adjustment in a direction orthogonal to an optical axis, rotation adjustment around an optical axis, slant angle adjustment, or others.
Conventionally, in order to realize the eccentricity adjustment in the state that lenses are fitted into the barrel, an eccentricity adjusting mechanism enabling the eccentricity adjustment by moving some lenses largely influencing the optical performance by using a tool or the like from the outside of the lens barrel has been suggested.
For example, according to the eccentricity adjusting mechanism of JP-A-2000-66076, some of a lens group having a plurality of lenses integrally held in an outer lens frame are held as lenses to be subjected to eccentricity adjustment in an inner lens frame disposed in the inside of the outer lens frame. The outer lens frame is axially supported by an eccentric pin engaged with the inner lens frame. The eccentric pin is rotated through a hole penetrating from the outside of the barrel to the eccentric pin, thereby adjusting a slant angle of the lenses in the inner lens frame.
According to the eccentricity adjusting mechanism of JP-A-2000-75182, a lens group having a plurality of lenses is held in the outer lens frame, as in JP-A-2000-66076. Some of the lens groups are held as lenses to be subjected to eccentricity adjustment in the inner lens frame. A gear is provided on the circumferential surface of the inner lens frame. The inner lens frame is rotated by a rotating means engaged with the gear through an aperture penetrating from the outside of the barrel to the gear, thereby adjusting rotation of the lenses of the inner lens frame around the optical axis.
According to the eccentricity adjusting mechanism of JP-A-H11-174301, an exposed part is provided in a lens frame holding lenses to be subjected to eccentricity adjustment in the direction orthogonal to the optical axis, and exposed from the outside of the barrel. The exposed part is displaced by an adjustment jig, thereby adjusting the position of the lenses in the direction orthogonal to the optical axis.
However, in case of providing the eccentricity adjusting mechanism for carrying out the eccentricity adjustment by adjusting the position of the lenses in the direction orthogonal to the optical axis, if the eccentricity adjusting mechanism is configured to form the exposed part to be exposed from the outside of the lens barrel in the lens frame of the lenses to be subjected to the eccentricity adjustment as in JP-A-H11-174301, the lens barrel needs to be forwardly and backwardly separable at the position of the lenses in order to insert the exposed part into the barrel and position it therein. In that case, in consideration of the structure of the lens barrel, the lenses to be subjected to the eccentricity adjustment are limited. Accordingly, eccentricity adjustment for lenses other than the lenses largely influencing the optical performance and most suitable for the eccentricity adjustment is carried out, or the structure of the lens barrel should be substantially modified in accordance with the position of the lenses most suitable for eccentricity adjustment.
In case of providing the eccentricity adjusting mechanism for holding an integrated lens group having a plurality of lenses in one lens frame in the state that the lenses are positioned in the optical axis direction with good accuracy, and adjusting the position of some of the lens group to be subjected to the eccentricity adjustment in the direction orthogonal to the optical axis, the mechanism set forth hereinafter may be considered. As in JP-A-2000-66076 and JP-A-2000-75182, among the lens group held in the outer lens frame, lenses to be subjected to the eccentricity adjustment are held by the inner lens frame. Screw holes are provided at a plurality of positions on the outer lens frame in the diameter direction and penetrate up to the inner lens frame. Screws are screwed into the screw holes. A hole is provided on the barrel while penetrating from the outside of the barrel to the screws. Each of the screws of the outer lens frame is rotatably adjusted through the hole from the outside of the barrel, so that the position of the lenses held in the inner lens frame can be adjusted in the direction orthogonal to the optical axis. Since the barrel has to only have the hole for rotatably adjusting the screws of the outer lens frame, even if the lenses largely influencing the optical performance and most suitable for eccentricity adjustment are part of the lens group integrally held in the lens frame, the mechanism for adjusting the eccentricity of the lenses can be easily provided in the lens barrel.
In the case of providing such eccentricity adjusting mechanism, when the eccentricity of the lenses held in the inner lens frame is adjusted, if the position of the optical axis direction or the slant angle of the lenses varies, setting the most optimum state would become difficult. Further, the optical performance may be deteriorated. Accordingly, a regulating means for regulating the inner lens frame to be displaced only in the direction orthogonal to the optical axis is required. The configuration disclosed in JP-A-2000-66076 and JP-A-2000-75182 may also be applied to the regulating means. According to the configuration, an engaging part is provided in the outer lens frame and inwardly projected in the diameter direction. The inner lens frame holding the lenses to be subjected to the eccentricity adjustment is inserted from an aperture (insertion aperture) on one side of the outer lens frame, such that the end of the inserted side of the inner lens frame or the lenses held in the inner lens frame is engaged with the engaging part. Accordingly, separation of the inner lens frame is prevented, and the optical axis direction is positioned. After the insertion of the inner lens frame, a circular elastic member such as a plate spring or rubber is inserted. Thereafter, a pressing ring screw-connected to the inner circumferential surface of the outer lens frame is screwed so that the inner lens frame and the elastic member are fixed in the state that they are sandwiched between the engaging part and the pressing ring. Accordingly, the inner lens frame is pressed toward the engaging part by the elastic member, so that the inner lens frame can be displaced in the direction orthogonal to the optical axis without varying the position of the optical axis direction or the slant angle.
However, the eccentricity adjusting mechanism having the configuration of JP-A-2000-66076 and JP-A-2000-75182 as described above requires the elastic member and the pressing ring. Accordingly, a more simple structure is demanded to reduce the number of components thereby reducing the number of fitting processes and costs.
The present invention has been made in consideration of the circumstances, and its object is to provide a lens barrel having an eccentricity adjusting mechanism for carrying out eccentricity adjustment by displacing some of a lens group having a plurality of lenses integrally held by an outer lens frame in a direction orthogonal to an optical axis, wherein the number of the components for the eccentricity adjusting mechanism is reduced thereby reducing the number of fitting processes and costs.